1. Field of the Invention
The present invention relates to a rotation controlling apparatus for controlling the rotation by utilizing a cam, and a sheet feeding system having such rotation controlling apparatus.
2. Related Background Art
In the past, the control of rotation in a driving mechanism such as rollers was effected by independent control motors, or clutches such as electromagnetic clutches or spring clutches. In a sheet feeding system used in a compact printer or copying machine, since it was required to control one revolution of a rotary element exactly and inexpensively, a spring clutch as shown in FIGS. 10 to 13 has generally been used.
Now, such spring clutch will be fully described.
In FIGS. 10 to 13, a sheet supply roller 101 is mounted on a roller holder 102. The roller holder 102 has a semi-circular cross-section and is fixedly or non-rotatably mounted on a sheet supply shaft 103 by means of a pin and the like (not shown). On the sheet supply shaft 103, there are mounted a rotatable input gear 105 rotated by a rotational force from an external driving system 104, and a boss 106 secured to the sheet supply shaft 103 and slightly spaced apart from the input gear. The input gear 105 and the boss 106 are provided at their confronting ends with cylindrical extensions 105a, 106a, respectively, having substantially the same diameters, and a spring 107 is mounted around these extensions with a slight gap therebetween. One end of the spring is bent toward an axial direction to be inserted into a hole formed in the boss 106. The spring 107 is so mounted that, when the input gear 105 is rotated, the spring is contracted to be urged against the extensions. The other end of the spring is cocked radially outwardly, so that it is engaged by a control ring 108 extending between and rotatably mounted around inner shoulders 105b, 106b of the input gear 105 and of the boss 106. The control ring 108 is provided at its peripheral surface with a pawl 108a by which a flapper 110 mounted on a solenoid 109 can be engaged. When the solenoid 109 is turned OFF, the flapper 110 is engaged by the pawl 108a, whereas, when the solenoid is turned ON, the flapper is disengaged from the pawl.
With this arrangement, when the solenoid 109 is turned OFF, since the spring 107 can be contracted inwardly toward the extension 105a of the input gear 105, the spring 107 tends to move together with the input gear. However, since the rotation of the end of the spring is regulated by the flapper 110 via the control ring 108, as shown in FIG. 13, the spring 107 is loosened until the spring 107 and the input gear 105 are slipped relative to each other, and, thereafter, this condition is maintained (clutch-off condition).
On the other hand, when the solenoid 109 is turned ON, since the flapper 110 is disengaged from the control ring 108, the spring 107 becomes a free condition. Thus, when the input gear 105 is rotated, the spring 107 is contracted to be firmly urged against the cylindrical extension 105a of the input gear 105 as shown in FIG. 12, with the result that the boss 106 is rotated integrally with the input gear 105, thus rotating the sheet supply roller 101 (clutch-on condition). By turning the solenoid 109 OFF again after the turning ON of the solenoid, the rotation of the control ring 108 is regulated again after one revolution of the sheet supply shaft 103, so that the rotation of the input gear is not transmitted to the boss. In this way, one revolution of the sheet supply roller is controlled.
However, in the above-mentioned conventional technique, since the spring 107 is always slidingly contacted with the cylindrical extension 105a, the following problems arose.
(1) Since the spring 107 acting as a driving force transmitting portion is slid on the cylindrical extension 105a, there arises a problem regarding the wear. Thus, the hardness of surfaces of the spring and the cylindrical extension must be adjusted, or the spring and the cylindrical extension must be made of special material such as sintered alloy. PA1 (2) In order to turn the clutch ON and OFF smoothly, the proper lubricant must be applied on the cylindrical extension 105a. PA1 (3) The proper clearance must be provided between the spring 107 and the cylindrical extension 105a.
If any one of these requirements (1)-(3) is insufficient, since the torque becomes unbalance, the spring clutch will generate unacceptable noise, poor torque transmission (slip) and/or sequential movement. Further, since the special material must be used, the apparatus is made expensive. Further, the assembling the adjustment of the apparatus become very difficult.